1. Field of the Invention
The present invention relates to a vertical support structure or tower for wind turbines generating electric energy or other uses, made of prestressed concrete, providing a frustoconical or cylindrical column shaft of prestressed concrete with variable height built by means of annular sectors, each of which comprises several wall pieces with a semicircular or polygonal section or semicircular or polygonal sectors, longitudinally attached to each other, and in the case of several superimposed in height, longitudinally attached with a system allowing the structural continuity of the tower. Either the wind turbine directly or another metal column shaft on which the turbine will finally be fixed will be located at its upper end.
This invention also has its application in the field of construction in general and especially in the industry for building and installing support structures for wind turbines generating electric energy.
A second aspect of the invention relates to a process for erecting the support structure or tower based on the successive incorporation of the mentioned wall pieces
Throughout the present specifically, wall piece will be understood as a piece forming the wall of the support structure or tower, being said wall thin, from 5 to 30 cm, made of prestressed concrete, with a centered prestressing and a non-prestressed reinforcement in the perimeter of the section or fiber-reinforced concrete, suitable for forming next to one or more pieces an annular sector of the support structure or tower.
2. Discussion of Related Art
In relation to the state of the art, it should be mentioned that the wind sector, which is widely expanding within the development of renewable energies, has gradually progressed in search of a greater cost-effectiveness, which has resulted in the design of increasingly more powerful wind turbines, of 3 or even 5 MW, to cover the demand created.
These new designs oblige rethinking the support structures or towers bearing the wind turbine, which must withstand stresses that are much greater than those today do and reach new heights of up to 120 m in order to be able to house machines with blades of more than 50 m in length.
An extrapolation of towers today (up to 70 m in height) built by means of curved and electrowelded plates, transversely attached by means of flanges, does not allow dealing with, in a cost-effective manner, the new features required of said elements, especially due to the enormous flexibility of this type of structures made of steel and to the incompatibility of this characteristic with the requirements extracted from the dynamic calculation of these new towers.
It is therefore necessary to use other materials and among them, concrete has the necessary characteristics for dealing with the aforementioned problems.
In this sense, there have been several initiatives that have already been undertaken: some solve the construction of these towers in reinforced concrete or performing a post-tensioning “in situ”, i.e., in the wind farm itself and in its final position, of these elements as a result of a slipform or climbing form. In the case of the post-tensioning “in situ”, cables are passed through and post-tensioned inside the thin concrete wall in jacket tubes left for that purpose either on the inside or outside of the tower. In addition to being expensive, these solutions have the problem of the long periods required for performing them, which works directly against the cost-effectiveness of the project.
In other cases, attempts have been made to solve the problem by means of small pieces made of prefabricated concrete such as circular voussoirs, or small plates (which are attached to each other forming the tower). These generally reinforced pieces require considerable thicknesses in order to assure the suitable dynamic operation of the tower once it is subjected to the service loads and accordingly with a cracked section. For this reason, these designs are occasionally reinforced by means of inner or outer post-tensioning operations performed in situ which compress all the sections along the tower to prevent cracking.
In this solution, the presence of a large number of attachments between pieces, of post-tensioning operations in situ, etc., greatly complicates and makes the assembly of these towers extremely expensive and compromises the actual operation of the assembly.
A number of background documents are known which describe various embodiments towers using reinforced concrete, among which the following should be mentioned: JP-A-9-235912, DE-A-29809541, DE-A-19832921, EP-A-960986, US2006/0254168, WO 02/01025, U.S. Pat. No. 7,114,295, JP-OR-3074144, EP-A-1474579 (MECAL APPLIED MECHANICS), EP-A-1645761 (INNEO21), EP-A-1876316 (MONTANER), WO2007/033991 (SIKA), WO2008/031912 8 (GAMESA).
The technical solutions explained in the mentioned patents can be classified into the following groups:
a. Tower built in situ.
b. Tower made of reinforced concrete with superimposed annular sectors, and post-tensioning in the field.
c. Towers made of concrete formed by the superimposition of annular structural sectors integrated in two or more assembled component parts which require post-tensioning in the field.
d. Lattice towers either made of concrete or steel.
e. Tower formed by concrete poured between steel sheets.
f. Towers in which pieces with different shapes which are suitable for either aiding in the production or improving the structural efficacy are provided;
g. Towers including pieces having incorporated therein specific reinforcement elements.
Patent FR 1145789 relates to a process for building a tower or stack without scaffolding with prefabricated elements. Despite the fact that the document indicates that said prefabricated elements can be made of prestressed concrete, when FIGS. 8 to 10 are described it is indicated that the vertical attachments will include prestressed ties which can be seen in said figures.
U.S. Pat. No. 5,809,711 describes an apparatus and a method for attaching two precompressed concrete elements that can form structures such as masts, towers or for example bridges. The patent describes prestressed concrete elements, in the form of wall pieces, connected with several prestressed strands which are prolonged extended out of the wall piece and inserted through ducts configured in a superimposed adjacent wall piece, which ducts run through virtually all of said adjacent piece, for the linking thereto by a subsequent tensioning of said extension strands, obtaining universal joints. This constructive solution has the drawback of being limited to developments of little height of the wall pieces, such as voussoir structures, since otherwise the on site assembly of the wall pieces, which must have the strands inserted therein for the post-tensioning of the entire wall piece and the attachment between superimposed wall pieces, would involve a very difficult and complicated operation.
The present invention proposes a vertical support structure or tower, of the type comprising several superimposed annular structural sections, each of which integrates two or more wall pieces attached at their longitudinal edges, and it is different from the previous proposals, which are generally based on the post-tensioning of cables at the actual point of installation of the tower or wind farm, to provide the tower and the attachment joints with strength, by the particularity of building the wall pieces by prestressing in the factory, calculated according to the relative position that the piece will occupy in the tower or structure, therefore the pieces forming the tower, by incorporating the prestressing, are already by themselves structurally resistant, requiring only performing the attachments between the adjacent and superimposed wall pieces to form the tower. Furthermore, costs are reduced by means of the proposal of this invention since prestressing in the factory is an industrial process and since it is not necessary to place post-tensioned cables in the field. On the other hand, the technology applied eliminates the need for auxiliary elements for transport, assures a state of compression in the pieces which maximizes the useful life of the tower, allows new designs and assembly alternatives which simplify obtaining the tower.
Another distinguishing aspect of the proposal on which the present invention is based lies in a connection system between prefabricated elements with pre-tensioned reinforcement, particularly applicable to the attachment of the annular sectors of the column shaft, which allows the continuity of the prestressing action without (complete or partial) need of additional elements such as bond bars or other post-tensioning systems, and compressing the diffusion end areas of each piece in the attachments, using its own prestressing cables which configure the prestressed reinforcement of the pre-tensioned wall pieces mentioned, but which unlike the solution explained in U.S. Pat. No. 5,809,711, only affects a short end sector of each piece in the areas of attachment of the superimposed pieces.
Other documents of the state of the art which can be cited are patents DE 20 2005 020398, EP 1876316, EP 758034, DE 102 23 429, and JP 2004 011210.
The singular aspects of the present invention are described below.